When WelcomeSurvey was created, the Growth team ran A/B testing with it to determine how it should display to the users as well as which questions should be included. WelcomeSurvey still has support A/B testing, which should be kept (for tasks like T342353). However, the configuration also includes list of legacy experiment groups, which doesn't need to be kept. The groups are as follows:

• exp1_group1 (all questions minus the languages one)
• exp1_group2 (no WelcomeSurvey)
• exp2_control (no WelcomeSurvey`)
• exp2_target_specialpage (regular WelcomeSurvey; this is the group we normally assign 100% of users to).

While at it, we probably should rename exp2_target_specialpage to something more descriptive, since this is de facto the control group those days. I suggest renaming it to control, in line with Homepage variants.

WelcomeSurvey also includes legacy code from T284127, which can be safely removed at this point.

It would be nice to complete this task together with T342353, to make the WelcomeSurvey configuration easier to read while touching it :).

Checklist

• Remove legacy experiment groups from WelcomeSurvey configuration (all but exp2_target_specialpage)
• Rename exp2_target_specialpage to control
• Remove B&C code introduced for T284127